JPH11233739A - Method for forming conductive film and manufacture of semiconductor storage device provided with it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a storage node with a small occupation area but a large surface area without depending on a film formation temperature and other heat treatment conditions. SOLUTION: When forming a storage node 24, polycrystalline silicon film 21 and a tungsten silicide film 22 and a tungsten silicide film 22 are successively deposited under a film formation condition where tungsten becomes excessive. Then, the tungsten silicide film 22 is heat-treated, thus oxidizing tungsten segregated at a crystal grain boundary. Then, etching is made under conditions where an oxide film is etched and tungsten oxide being formed at the crystal grain boundary is etched. Then, etching is made under conditions where the polycrystalline silicon film 21 is etched faster than the tungsten silicide film 22, thus forming a number of small holes 23 on the surface of the polycrystalline silicon film 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a conductive film and a method for manufacturing a semiconductor memory device provided with the same. For example, the present invention is particularly suitable for a semiconductor memory device having a memory capacitor such as a DRAM. is there.

[0002]

2. Description of the Related Art Recently, miniaturization and high integration of a semiconductor memory represented by a DRAM have been advanced. Along with this, for example, the electrode area occupied by a memory capacitor of a DRAM on a semiconductor substrate is reduced, and it is difficult to obtain a sufficient capacitor capacity. As a prominent method to address this problem, amorphous silicon (amorphous silicon) is used as the material of the lower electrode (storage node electrode) of the memory capacitor, and after the lower electrode is formed, growth nuclei are added to the surface thereof, and heat treatment is performed. A technique has been proposed in which the surface of the lower electrode is made uneven by applying it. By forming the lower electrode in this manner, the surface area thereof is greatly increased, and a large capacitor capacity can be obtained.

[0003]

However, according to the above-described method, it is possible to form the amorphous silicon film at a film forming temperature and other heat treatment conditions for obtaining a large capacitor capacity, that is, to make the surface uneven. There is a serious problem that the film forming temperature of the amorphous silicon film and other heat treatment conditions are within a very limited range, and the forming process is unstable.

Accordingly, an object of the present invention is to make it possible to easily form a lower electrode of a memory capacitor having a small occupied area and a large surface area without depending on a film forming temperature or other heat treatment conditions. It is an object of the present invention to provide a method for manufacturing a highly reliable semiconductor memory device which meets the further miniaturization and high integration of a semiconductor memory which is a demand of the above.

Another object of the present invention is to provide a conductive film capable of easily forming a lower electrode of a memory capacitor having a small occupied area and a large surface area without depending on a film forming temperature or other heat treatment conditions. Is to provide a method of manufacturing the same.

[0006]

A method of forming a conductive film according to the present invention is a method of forming a conductive film formed in a predetermined pattern on an upper layer of a semiconductor substrate, wherein a polycrystalline silicon film and a tungsten silicide film are sequentially laminated. A first step of performing a heat treatment on the tungsten silicide film, and a third step of etching the entire surface of the tungsten silicide film and the polycrystalline silicon film until the tungsten silicide film is removed. Including.

In one embodiment of the method for forming a conductive film according to the present invention, in the first step, when forming the tungsten silicide film, the film forming conditions are such that tungsten becomes excessive.

In one embodiment of the method for forming a conductive film according to the present invention, in the third step, first, a first etching is performed under the condition that an oxide film is etched, and then the first etching is performed in comparison with the tungsten silicide film. Then, the second etching is performed under the condition that the polycrystalline silicon film is rapidly etched.

A method of manufacturing a semiconductor memory device according to the present invention includes an access transistor having a gate and a pair of impurity diffusion layers, and a memory capacitor in which a lower electrode and an upper electrode are capacitively opposed to each other via a capacitive insulating film. A method of manufacturing a semiconductor memory device comprising: a first step of sequentially stacking a polycrystalline silicon film and a tungsten silicide film; a second step of heat-treating the tungsten silicide film; and removing the tungsten silicide film. Until this, a third step of etching the entire surface of the tungsten silicide film and the polycrystalline silicon film and a fourth step of processing the polycrystalline silicon film to form the lower electrode are included.

In one embodiment of the method of manufacturing a semiconductor memory device according to the present invention, after the fourth step, a fifth step of forming the capacitor insulating film so as to cover the lower electrode;
A sixth step of forming the upper electrode covering the lower electrode with the capacitance insulating film interposed therebetween.

In one embodiment of the method of manufacturing a semiconductor memory device according to the present invention, in forming the tungsten silicide film in the first step, the tungsten silicide film is formed under such a condition that tungsten becomes excessive.

In one embodiment of the method of manufacturing a semiconductor memory device according to the present invention, in the third step, first, a first etching is performed under the condition that an oxide film is etched, and then the tungsten silicide film is etched. The second etching is performed under the condition that the polycrystalline silicon film is etched faster.

[0013]

In the present invention, first, a polycrystalline silicon film and a tungsten silicide film are sequentially laminated. Here, when the tungsten silicide film is formed, for example, by setting the film formation conditions in which tungsten becomes excessive, the tungsten segregates at the crystal grain boundary of the tungsten silicide film. Next, the tungsten silicide film is heat-treated. At this time, the tungsten segregated at the crystal grain boundaries is oxidized, and the crystal grain boundaries become remarkable.
Thereafter, the entire surface of the tungsten silicide film is etched.
Specifically, first, etching is performed under the condition that the oxide film is etched. At this time, the tungsten oxide generated at the crystal grain boundary of the tungsten silicide film by the heat treatment is etched. Subsequently, etching is performed under the condition that the polycrystalline silicon film is etched faster than the tungsten silicide film. At this time, the tungsten silicide film in the portion of the crystal grain boundary is thinned by the above-described etching of the tungsten oxide, and the etching of the lower polycrystalline silicon film starts before the other portions. Since the etching rate of the polycrystalline silicon film is higher than that of the tungsten silicide film, well-shaped fine holes are formed in the polycrystalline silicon film, and the upper surface of the polycrystalline silicon film becomes uneven.

As described above, according to the present invention, a polycrystalline silicon film is formed in which a large number of well-shaped fine holes are formed on the upper surface to form an uneven surface. This polycrystalline silicon film has a large surface area even if its occupied area is small due to the micropores. Therefore, by forming this polycrystalline silicon film as, for example, a lower electrode of a memory capacitor, a memory capacitor having a large capacitor capacity in an extremely narrow region on a semiconductor substrate is realized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific embodiment in which a method for forming a conductive film according to the present invention and a method for manufacturing a semiconductor storage device according to the present invention will be described in detail with reference to the drawings.

In the present embodiment, a DRAM having a so-called CUB (Capacitor Under Bitline) structure having an access transistor and a memory capacitor as a semiconductor memory device and in which the memory capacitor is formed substantially below a bit line is exemplified. The configuration will be described together with the manufacturing method. 1 and 2 are schematic cross-sectional views showing a method for manufacturing a DRAM of the present embodiment in the order of steps.

First, as shown in FIG.
A field oxide film 13 is formed as an element isolation structure on a silicon semiconductor substrate 11 of a mold by a so-called LOCOS method to define an element formation region. Instead of the field oxide film 13, a conductive film is buried in the oxide film by a field shield element isolation method, and a portion of the silicon semiconductor substrate immediately below is fixed at a predetermined potential by the conductive film to perform element isolation. May be formed.

Then, a heat treatment is applied to the surface of the silicon semiconductor substrate 11 in the element formation region which is separated from each other by the field oxide film 13 to form a thermal oxide film. The polycrystalline silicon film and the silicon oxide film thus formed are deposited.

Next, the thermal oxide film, the polycrystalline silicon film and the silicon oxide film are patterned by photolithography and subsequent dry etching, and the thermal oxide film, the polycrystalline silicon film and the silicon oxide film are formed into an electrode shape in the element forming region. The gate oxide film 12, the gate electrode 15, and the cap insulating film 16 thereof are formed by patterning.

Next, after removing the photoresist used for patterning by ashing, the silicon oxide film is deposited and formed on the entire surface including the gate electrode 15 by the CVD method. Etching is performed to form sidewalls 17 while leaving the silicon oxide film only on the side surfaces of the gate oxide film 12, the gate electrode 15, and the cap insulating film 16 thereof.

Next, using the cap insulating film 16 and the side walls 17 as a mask, n is implanted into the surface region of the silicon semiconductor substrate 11 on both sides of the gate electrode 15 by ion implantation.
By introducing a type impurity, a pair of impurity diffusion layers 10 serving as a source / drain are formed, and an access transistor having the gate electrode 15 and the pair of impurity diffusion layers 10 is completed.

Subsequently, as shown in FIG. 1B, a silicon oxide film is deposited and formed on the entire surface of the silicon semiconductor substrate 11 including the field oxide film 13 by a CVD method, and the surface is flattened to thereby form an interlayer insulating film. The film 14 is formed. continue,
The interlayer insulating film 14 is patterned by photolithography and subsequent dry etching to form a storage contact hole 18 exposing a part of the surface (usually a source) of one of the pair of impurity diffusion layers 10.

Next, as shown in FIG. 1C, the entire surface of the interlayer insulating film 14 including the inside of the storage contact hole 18 has C
A polycrystalline silicon film 21 is deposited and formed under normal film forming conditions by a VD method, and then a tungsten silicide film 22 is laminated on the polycrystalline silicon film 21 by a CVD method. The conditions for forming the tungsten silicide film 22 are set so that tungsten is excessive and the crystal grain size is, for example, about 0.2 μm. Therefore, excessive tungsten in the formed tungsten silicide film 22 segregates at the crystal grain boundaries of the tungsten silicide film 22.

Subsequently, a heat treatment is performed on the tungsten silicide film 22 in an oxidizing atmosphere. This heat treatment oxidizes the tungsten segregated at the crystal grain boundaries and makes the crystal grain boundaries prominent.

Subsequently, the entire surface of the tungsten silicide film 22 is anisotropically etched. Specifically, first, etching is performed under the condition that the oxide film is etched. At this time, the tungsten oxide generated at the crystal grain boundaries of the tungsten silicide film 22 by the heat treatment is etched. Subsequently, etching is performed under the condition that the polycrystalline silicon film 21 is etched faster than the tungsten silicide film 22. At this time, the tungsten silicide film 22 in the portion of the crystal grain boundary is thinned by the above-described etching of the tungsten oxide,
Etching of the lower polycrystalline silicon film 21 starts prior to other portions. Since the etching rate of the polycrystalline silicon film 21 is higher than that of the tungsten silicide film 22, as shown in FIG. 2A, the surface of the polycrystalline silicon film 21 exposed by removing the tungsten silicide film 22 has The fine holes 23 are formed, and the upper surface of the polycrystalline silicon film 21 becomes an uneven surface.

Subsequently, as shown in FIG. 2B, the polycrystalline silicon film 21 is patterned into an electrode shape by photolithography and subsequent dry etching to form a storage node electrode 24. Since the storage node electrode 24 has an uneven surface with a large number of fine holes 23 formed on the upper surface as described above, it has an extremely large surface area even though the occupied area is small. Specifically, one storage node electrode 24 is connected to the silicon semiconductor substrate 11
The area occupied on the top is about 1.0 μm ² and the thickness is 0.5
μm, the diameter of the fine holes 23 is about 0.05 μm,
3 has a depth of about 0.3 μm and a density of the fine holes 23 of about 36 / μm ^2.
In this case, the surface area of the storage node electrode 24 is increased to about 1.6 times that of the conventional storage node electrode having the same occupied area.

Subsequently, as shown in FIG. 2C, a three-layer structure film of a silicon oxide film / silicon nitride film / silicon oxide film and a polycrystalline silicon film are formed so as to cover the storage node electrode 24 by the CVD method. Are sequentially deposited and subjected to predetermined patterning to form an ONO film 25 and a cell plate electrode 26. Here, the storage node electrode 24 and the ONO film 25
And a cell plate electrode 26, and a storage capacitor is completed in which the storage node electrode 24 and the cell plate electrode 26 face each other via an ONO film 25 which is a capacitance insulating film (dielectric film) and are capacitively coupled.

Thereafter, although not shown, further formation of an interlayer insulating film, formation of a connection hole and subsequent formation of a wiring layer (bit line and the like), formation of a peripheral circuit portion of a memory cell portion (this peripheral circuit portion) Section is often formed sequentially with the memory cell section) to complete the DRAM.

As described above, in the present embodiment, a polycrystalline silicon film 21 having a large number of well-shaped fine holes 23 formed on the upper surface to form an uneven surface is formed. The polycrystalline silicon film 21 has a large surface area even though its occupied area is small due to the fine holes 23. Therefore, by forming storage node electrode 24 from polycrystalline silicon film 21, a memory capacitor having a large capacitor capacity in an extremely narrow region on silicon semiconductor substrate 11 is realized.

That is, according to the present embodiment, the storage node electrode 24 of the memory capacitor having a small occupied area and a large surface area can be easily formed without depending on the film forming temperature and other heat treatment conditions. A highly reliable DRAM meeting the recent demands for further miniaturization and high integration is manufactured.

[0031]

According to the present invention, it is possible to easily form a lower electrode of a memory capacitor having a small surface area and a large surface area without depending on the film forming temperature or other heat treatment conditions. It is possible to provide a highly reliable semiconductor memory device that meets the further miniaturization and high integration of the semiconductor memory, which is a requirement.

Further, according to the present invention, it is possible to easily form a conductive film having a small occupied area and a large surface area without depending on the film forming temperature and other heat treatment conditions.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a method for manufacturing a DRAM according to an embodiment of the present invention.

FIG. 2 is a continuation of FIG. 1 showing D in an embodiment of the present invention;
FIG. 4 is a schematic sectional view illustrating a method for manufacturing a RAM.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Impurity diffusion layer 11 Silicon semiconductor substrate 12 Gate oxide film 13 Field oxide film 14 Interlayer insulating film 15 Gate electrode 16 Cap insulating film 17 Side wall 18 Storage contact hole 21 Polycrystalline silicon film 22 Tungsten silicide film 23 Micro hole 24 Storage node electrode 25 ONO film 26 Cell plate electrode

Claims (7)

[Claims] 1. A method for forming a conductive film formed in a predetermined pattern on an upper layer of a semiconductor substrate, comprising: a first step of sequentially laminating a polycrystalline silicon film and a tungsten silicide film; and heat treating the tungsten silicide film. A method for forming a conductive film, comprising: a second step; and a third step of etching the entire surface of the tungsten silicide film and the polycrystalline silicon film until the tungsten silicide film is removed. 2. The method for forming a conductive film according to claim 1, wherein, in forming the tungsten silicide film in the first step, a film forming condition is such that tungsten becomes excessive. 3. In the third step, first, the first etching is performed under the condition that the oxide film is etched, and then the polycrystalline silicon film is etched faster than the tungsten silicide film. The method according to claim 1, wherein the second etching is performed. 4. A method for manufacturing a semiconductor memory device, comprising: an access transistor having a gate and a pair of impurity diffusion layers; and a memory capacitor in which a lower electrode and an upper electrode are capacitively coupled to each other via a capacitive insulating film. A first step of sequentially laminating a polycrystalline silicon film and a tungsten silicide film; a second step of heat treating the tungsten silicide film; and the step of removing the tungsten silicide film until the tungsten silicide film is removed. A method of manufacturing a semiconductor memory device, comprising: a third step of etching the entire surface of a polycrystalline silicon film; and a fourth step of processing the polycrystalline silicon film to form the lower electrode. 5. A fifth step of forming the capacitive insulating film so as to cover the lower electrode after the fourth step, and forming the upper electrode covering the lower electrode with the capacitive insulating film interposed therebetween. The method according to claim 4, further comprising: performing a sixth step. 6. The semiconductor memory device according to claim 4, wherein, in forming the tungsten silicide film in the first step, a film forming condition is such that tungsten becomes excessive. Method. 7. In the third step, first, the first etching is performed under the condition that the oxide film is etched, and then the polycrystalline silicon film is etched faster than the tungsten silicide film. 7. The method of manufacturing a semiconductor memory device according to claim 4, wherein the second etching is performed.